This got me thinking... I wonder how hard it would be to create a service that scours the web and detects the influence of PR (versus organic) for a given brand

This got me thinking... I wonder how hard it would be to create a service that scours the web and detects the influence of PR (versus organic) for a given brand. If you somehow measured the "sentiment" of each article towards a brand, perhaps by scanning for words, weighing each one and compiling a score for a given article, you might able to chart the total score for that brand over time. For instance, too many positive articles that get published "out of the blue" (unprompted by events) would strongly hint at a PR team at work.